Method for the Cold Deformation of a Continuous Metal Strip

ABSTRACT

The invention relates to the pressure treatment of metals, specifically to producing a metal strip using cold deformation. A strip is consecutively drawn with back and front tension through bending devices. Moreover, the degree of deformation of a strip is regulated in each bending device by means of changing the ratio of the speed of the strip exiting a bending device to the speed of said strip entering said device, in such a way as to avoid a break in the metal, the required number of bending devices being selected on the basis of the total stretch factor of a strip and on the maximum allowable stretch factor of same. The result is increased deformation of a strip and reduced energy consumption.

RELATED APPLICATIONS

This Application is a Continuation application of International Application PCT/RU2012/000615, filed on Jul. 27, 2012, which is incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The invention relates to the processing of metals without machining, in particular, to the production of a metal strip by cold deformation.

BACKGROUND OF THE INVENTION

A method of cold deformation of a continuous metal strip is known in the manufacture of seamed tubes, including the drawing of the strip by a pulling mechanism between three non-driven rollers of a bending device, wherein the middle roller, having a diameter less than the diameter of the outer rollers, together with the strip encircling more than 180° of its circumference, is forced by the tension of the strip against the outer rollers having a gap between them greater than two thicknesses of the strip (USSR Inventor's Certificate No. 1500405, pub. Aug. 15, 1989).

A disadvantage of the known method is the lack of control over the magnitude of the deformation of the strip.

A method of cold deformation of a continuous metal strip is known in the manufacture of seamed tubes, including the application of backward and forward tension created respectively by tensioning and pulling mechanisms to draw the strip between three non-driven rollers of a bending device, wherein the middle roller has a diameter less than the diameter of the outer rollers, is encircled by the strip to more than 180° of its circumference and is forced together with the strip, by the tension of the strip, against the outer rollers having a gap between them greater than two thicknesses of the strip, with the ability to regulate the magnitude of the deformation of the strip by adjusting its tension while maintaining the forward tension below the level of tensile stress in the drawn strip corresponding to 0.85 of the tensile yield strength of its metal (Russian patent for invention No. 2412016, pub. Feb. 20, 2011)—the prototype.

The prototype provides the ability to regulate the magnitude of the deformation of the strip, but its disadvantage is the low magnitude of strip deformation and the increased specific energy consumption per unit of strip deformation.

BRIEF DESCRIPTION OF THE DRAWINGS FIGURE

FIG. 1 is a schematic illustration of a structure for implementing a method of cold deformation of a continuous metal strip.

SUMMARY OF THE INVENTION

The aim of the present invention is to increase the magnitude of the strip deformation and to decrease the specific energy consumption per unit of strip deformation.

The technical result is achieved by the fact that the method for cold deformation of a continuous metal strip includes drawing of the strip under backward and forward tension between three non-driven rollers of each bending device, wherein the middle roller, having a diameter less than the diameter of the outer rollers, is encircled by the strip to more than 180° of its circumference and is forced together with the strip, by the tension of the strip, against the outer rollers having a gap between them greater than two thicknesses of the strip, with the ability to regulate the magnitude of the deformation of the strip by adjusting its tension while maintaining the forward tension below the level of tensile stress in the drawn strip corresponding to 0.85 of the tensile yield strength of its metal. The novelty of the method is in fact that the strip is successively drawn through a group of bending devices comprising, at least, two bending devices, and through each of the separate bending devices, at least, through one separate bending device. The strip is drawn under backward and forward tension in each bending device of the group and in each separate bending device. The drawing is effected by means of a tensioning device mounted before the inlet side of the first bending device of the group in the process stream, auxiliary pulling devices, the first of which is mounted at the exit side of the last bending device of the group and all the rest are placed at the exit side of each separate bending device except the last one, and the pulling device mounted at the exit side of the last separate bending device. Here, the magnitude of strip deformation is regulated in the group of bending devices and in each separate bending device within ranges, the upper boundary of which does not exceed the maximum permissible elongation ratio of the strip, respectively, for the group of bending devices and for each separate bending device. Deformation is regulated therein by change of the ratios, respectively, of the speed of the strip exiting the last bending device of the group to the speed of its entry into the first bending device of the group, and the speed of the strip exiting each separate bending device to the speed of its entry into that bending device.

Compared with the prototype, the magnitude of strip deformation is increased several fold, and the specific energy consumption per unit of strip deformation is decreased several fold in the proposed method. Moreover, the higher is the number of bending devices in the group and the higher is the number of separate bending devices, up to the optimal limit, the greater will be the magnitude of the strip deformation and the reduction in the specific energy consumption per unit of its deformation.

As the number of bending devices in the group increases, the increase in deformation and the reduction in the specific energy consumption are diminishing, while their operating costs increase; therefore, the number of bending devices in the group is selected on the basis of the lowest total costs.

Reduction of specific energy consumption per unit of strip deformation increases as the number of bending devices in the group increases because, given the constant magnitude of the forward tension, the total deformation of the strip in this group of devices increases. In addition, a significant portion of the forward tension, on the order of 80%, which remains after overcoming the resistance to its deformation in the last bending device of the group, is forward tension that draws the strip through the remaining bending devices of the group. Due to the reduction in the magnitude of the forward tension of the strip drawing it out of the penultimate bending device of the group, the magnitude of strip deformation therein is substantially lower than in the last bending device of the group; however, it increases the total deformation of the strip in the group of bending devices, thereby reducing the specific energy consumption per unit of its overall deformation. Additional increase in the number of the bending devices in the group (above these two devices) will increase the magnitude of strip deformation therein, which will additionally reduce the specific energy consumption per unit of its deformation. An increase in the number of bending devices within the group reduces the magnitude of the required backward tension of the strip applied by the tensioning device.

As a result of the proposed sequential deformation of the strip in separate bending devices, a significant part (about 80%) of its forward tension that remains unexpended after overcoming the resistance to deformation of the strip in each separate bending device is the main component of another forward tension that draws the strip from the preceding separate bending device or a group of bending devices. The magnitude of this other forward tension is equal to the sum of said forward tension component and the tractive force of the auxiliary pulling device. The tractive force of the auxiliary pulling device is approximately 4 times less than said forward tension component. That is, the sequential deformation of the strip in the separate bending devices with the use of auxiliary pulling devices required to add forward tension up to the required specification makes it possible to provide a high degree of deformation in each of these separate bending devices. With said sequential deformation of the strip, the reduction in the specific energy consumption per unit of strip deformation is greater the larger is the number of separate bending devices and the corresponding number of auxiliary pulling devices.

The maximum permissible strip elongation ratio, both in the group of bending devices and in each remaining separate bending device, depends mainly on the ratio of the strip thickness to the diameter of the middle roller. The greater the thickness of the strip and smaller the diameter of the middle roller, the greater is the maximum permissible elongation ratio of the strip.

Furthermore, the maximum permissible elongation ratio of the strip in the group of bending devices depends on their number in the group. The greater their number in the group, up to an optimum limit, the greater the maximum permissible elongation ratio of the strip in the group of bending devices.

The required number of separate bending devices depends on the specified overall elongation ratio of the strip and on the maximum permissible elongation ratio of the strip, both in the group of bending devices and in each of the remaining separate bending devices.

The drawing shows a diagram of the embodiment of the proposed method of cold deformation of a metal strip by means of a tensioning device, a group of bending devices comprising two bending devices, three separate bending devices, three auxiliary pulling devices, and a pulling device.

DETAILED DESCRIPTION AND AN EMBODIMENT OF THE INVENTION

By means of a tensioning device 1, auxiliary pulling devices 2, 3, 4, and pulling device 5, a continuous metal strip 6 is being sequentially drawn under backward and forward tension between three non-driven rollers of each bending device 7 and 8 of a group and each separate bending device 9, 10, and 11.

Part of the tractive force of pulling device 5 is expended to overcome the resistance to the deformation of strip 6 in bending device 11. The remaining part of this tractive force helps auxiliary pulling devices 4, 3, and 2 to overcome the resistance to the deformation of strip 6 in bending devices 10, 9, 8, and 7 and the resistance of tensioning device 1. This remaining part of the tractive force of pulling device 5 is simultaneously the backward tensioning of strip 6 at the point of its entry into bending device 11.

Similar action occurs during the deformation of the strip in the remaining bending devices. For example, part of the total tractive force, including the tractive force of auxiliary pulling device 3 and the part of the tractive force of auxiliary pulling device 4 and of pulling device 5 remaining after deformation of strip 6 in bending devices 10 and 11, is expended to overcome the resistance to the deformation of strip 6 in bending device 9. The remaining part of this total tractive force helps auxiliary pulling device 2 to overcome the resistance to the deformation of strip 6 in the group of bending devices 8 and 7 and the resistance of tensioning device 1. This remaining part of the total tractive force is simultaneously the backward tensioning of strip 6 at the point of its entry into bending device 9.

The magnitude of the deformation of strip 6 in the group of bending devices 7 and 8 is regulated by changing the ratio of its exit speed from this group, which is provided by auxiliary pulling device 2, to its entry speed into this group of bending devices, provided by tensioning device 1. This change is effected within a range, the upper boundary of which does not exceed the maximum permissible strip elongation ratio in this group of bending devices. That maximum elongation ratio of the strip at which the process of deformation is achieved without rupture is the maximum permissible.

The magnitude of the deformation of strip 6 in each separate bending device 9, 10, and 11 is regulated by changing the ratio of its exit speed from the corresponding bending device to its entry speed into this device. The regulation is effected within a range, the upper boundary of which does not exceed the maximum permissible strip elongation ratio for each of these bending devices. The exit speed of the strip from

each bending device 9, 10, and 11 is regulated, respectively, with the aid of auxiliary pulling devices 3 and 4 and of pulling device 5. The entry speed of the strip into each bending device 9, 10, and 11 is regulated with the aid of auxiliary pulling devices, respectively, 2, 3, and 4.

The overall deformation magnitude of the continuous initial strip is regulated so as to obtain, after deformation, its specified thickness regardless of the longitudinal gage variability of the initial strip.

The following approach to regulating the overall deformation of the strip is preferred.

Constant exit speed of strip 6 from bending device 8 of the group is provided with the aid of auxiliary pulling device 2, while the entry speed of the strip 6 into bending device 7 of the group is regulated with the aid of tensioning device 1, depending on the thickness of the initial strip at the inlet of this bending device. This regulation is effected such that the thickness of the strip at the exit from bending device 8 of the group would be constant regardless of the initial longitudinal gage variability of the strip. In the process of regulation, the ratio of the exit speed of strip 6 from bending device 8 to its entry speed into bending device 7 is maintained within a range, the upper boundary of which does not exceed the maximum permissible elongation ratio of strip 6 in the group of bending devices 7 and 8.

The constant exit speed of strip 6 from each of the remaining separate bending devices, respectively 9, 10, and 11, is maintained with the aid of auxiliary pulling devices 3 and 4 and pulling device 5, and the strip elongation ratio in each of the bending devices will not exceed its maximum permissible value. These strip speeds are selected so as to afford an overall elongation ratio of the strip in all bending devices 7, 8, 9, 10, and 11, sufficient to obtain the required thickness of the finished strip.

With deformation of a strip by the proposed method, involving it being drawn through a group of bending devices comprising two bending devices and through each of three separate bending devices, the deformation of the strip, measured by the magnitude of its elongation in an experiment, increased 4.4-fold by comparison with the prototype, with a 1.6-fold increase in the total consumption of energy; the specific energy consumption per unit of deformation of the strip decreased 2.8-fold. Thus, the proposed method for cold deformation of a continuous metal strip, by comparison with the prototype, affords a several-fold increase in the magnitude of strip deformation and a several-fold decrease in the specific energy consumption for its deformation. Owing to this, the method can be used in place of cold rolling of a metal strip.

The use of the proposed method in place of cold rolling of a metal strip will make it possible to reduce capital expenditures associated with acquisition of equipment and construction of plant for strip deformation, substantially decrease wear on deformation tools, reduce the surface roughness of the strip, increase accuracy of strip manufacture with respect to thickness, and reduce energy consumption for strip deformation.

Substantiation of each of the advantages of the above-mentioned proposed method of cold deformation of a continuous metal strip as compared with cold rolling is presented below.

Given identical deformation parameters for the same metal strip, the pressure of the metal against the rollers in cold rolling is approximately 5-8 times greater than the pressure of the metal against the outer rollers of the bending device in cold deformation according to the proposed method. Therefore the weight of the equipment for cold deformation of a continuous metal strip according to the proposed method will be several times lower than the weight of the continuous cold rolling mill equipment. Accordingly, the cost of the equipment and the cost of plant construction will be several times lower as compared with the cost of the equipment and the cost of construction of the continuous rolling mill.

During cold rolling of a metal strip, in the deformation region, strip velocity in the backward creep zone is slower and in the forward creep zone is faster than the surface velocity of the working roll. Slippage of the strip relative to the rolls in said zones of the deformation region and the high roll-separating forces result in heavy wear of the rolls.

During strip deformation according to the proposed method, the rollers of each bending device create two deformation regions that are situated in the reversing areas of the strip bending direction. In these regions, the strip is subjected to shear deformation essentially without slippage relative to the rollers. The absence of strip slippage relative to the rollers and the decrease in the roll-separating forces result in reduction of roll wear by dozens of times as compared with their wear in cold rolling of a strip. This will also make it possible to ensure low surface roughness of the strip. This especially affects the surface in contact with the middle rollers of the bending devices, since the middle rollers have a small diameter and, therefore, afford good processing of the strip surface.

Methods used in the industry provide high accuracy of drive speed regulation. Therefore, regulation of strip deformation by controlling the speed of the drives of the tensioning device, the auxiliary pulling devices, and the pulling device will provide high accuracy of strip deformation in bending devices and, consequently, high accuracy of strip manufacture with respect to thickness.

It is known that, given identical deformation parameters of the same metal strip by different methods, minimal expenditures of energy occur with the use of the shear deformation method, which in fact is used in the proposed method. In addition, slippage of the deformable metal relative to the rollers is absent in the proposed method of strip deformation; this eliminates the expenditure of energy to overcome the frictional forces arising in the event of such slippage, which does take place with strip rolling.

As compared with cold rolling of a continuous metal strip, the proposed method of cold deformation of a continuous metal strip makes it possible to reduce the expenditure of energy for its deformation by approximately 15-35%. Further, the magnitude of energy savings increases with decreasing the diameter of the middle rollers of the bending devices and with increasing, up to the optimal limit, the number of bending devices in their group situated in between the tensioning device and the first auxiliary pulling device in the process stream. 

What is claimed is:
 1. A method for cold deformation of a continuous metal strip, comprising: drawing the strip under backward and forward tension between three non-driven rollers of a bending device, wherein a middle roller with a diameter less than a diameter of outer rollers is encircled by the strip to more than 180° of its circumference and is forced together with the strip, by a tension of the strip, against the outer rollers having a gap between them greater than two thicknesses of the strip; regulating a magnitude of deformation of the strip by adjusting its tension while maintaining the forward tension below the level of tensile stress in the strip corresponding to 0.85 of a tensile yield strength of its metal; wherein drawing the strip comprises sequentially drawing the strip under the backward and forward tension in each bending device first through: a plurality of bending devices comprising at least two bending devices, and then through at least one separate bending device by means of a tensioning device mounted before an inlet side of a first bending device of the plurality of the bending devices in the process stream; auxiliary pulling devices, the first one of which is mounted at an exit side of the last bending device of the plurality of the bending devices, and each of the remaining auxiliary pulling devices is mounted at an exit side of each separate bending device except the last one; and a pulling device mounted at the exit side of the last separate bending device; and wherein a magnitude of deformation of the strip is controlled, in the plurality of bending devices and in each separate bending device within ranges characterized by an upper boundary not exceeding a maximum permissible elongation ratio of the strip for the plurality of bending devices and for each separate bending device, respectively, by changing a ratio of an exit speed of the strip from the last bending device of the plurality to its entry speed into the first bending device of the group, and a ratio of the exit speed of the strip from each separate bending device to its entry speed into that bending device, respectively. 